In surgery, it is known to employ biodegradable, elongated, typically tubular surgical implants and devices for supporting or combining or dividing elongated organs, tissues or parts thereof. These objects include various canals, ducts, intestines, blood vessels, tubes, such as bronchial tubes, urinary tracts, nerves etc.
In this context, the biodegradable material refers to a material manufactured of polymer, copolymer or polymer composition, the degradation and/or absorbing of which material takes place by means of metabolic reactions and/or secretion through kidneys, lungs or intestines or skin.
A multitude of publications describe various tubular implants and surgical devices manufactured of biostable or biodegradable materials. Such implants are disclosed e.g. in publications U.S. Pat. Nos. 3,108,357; 3,155,095; 3,272,204; 3,463,158; 3,620,218; WO 83/03752; WO 84/03035; Daniel and Olding, Plast. Rec. Surg. 74 (1984) 329; WO 90/04982; Van Andersdahl et al., Seminars in Urology, Vol. II (1984) 180; Raja Subra Manian, ASAIO Journal 40 (1994) M584; U.S. Pat. Nos. 4,768,507; 4,923,470; 4,973,301; 4,990,131; 4,994,066; 5,019,090; EP-0 606 165 A1; WO 04/15583; U.S. Pat. Nos. 4,950,258; 5,160,341 and 5,085,629.
Known biostable, that is, in tissues practically non-degradable implants and surgical devices of the above mentioned and corresponding type have several shortcomings. Their biostable parts, e.g. fibres, plastic and metal threads or rings or tubes or the like remain in the system even after an organ or a tissue has healed, and therefore such implants and devices can later be harmful to the patient, causing e.g. infections, inflammatory reactions, foreign body reactions and/or particles or corrosion products or the like can be released therefrom, which can further cause harmful reactions in the system.
Known biodegradable implants and surgical devices and devices of a corresponding type, e.g. of the type disclosed in the above-mentioned publications, do not cause the same kind of chronic complications as biostable implants and surgical devices, since biodegradable implants and devices absorb and degrade entirely in the system finally leaving the tissue entirely.
However, typically tubular implants and surgical devices involve the drawback that they degrade evenly at their entirely length, that is, the gradient of biodegration is directed to the centre of the cross section along the entire length of the implant or the corresponding surgical device. Thus, known elongated implants and surgical devices lose their strength evenly at their entire length, and finally the whole implant or surgical device loses its strength in a relatively short period of time at its entire length. As a result, the implant or the surgical device disintegrates evenly after having lost its strength in a short period of time or even suddenly to small pieces and particles [cf. e.g. Tormala et al. Biomed. Mater. Res. 25 (1991) 1]. In case the disintegrating implant or surgical device is placed inside a hollow, elongated organ or tissue, it is possible that an uncontrollable quantity of particles and pieces is released from the disintegrating implant or the surgical device in a short period of time, wherein some of these parts and particles can join together and can contribute to a stoppage in the hollow tissue or organ, such as in a flow duct of a blood vessel, urinary tract or other tubular organ or tissue.